Token request on Exact Online not returning access token

I have been trying to use OAuth 2.0 to connect to Exact Online. We tend to focus on Java-applications and sadly Exact doesn't have documentation/examples/support for Java.

I was able to do the authentication request but for the token request I'm having some trouble. My code:

OAuthAuthzResponse oar = OAuthAuthzResponse.oauthCodeAuthzResponse(request);
        code = oar.getCode();

        OAuthClientRequest oAuthRequest;
        try {
            oAuthRequest = OAuthClientRequest
                    .tokenLocation("https://start.exactonline.be/api/oauth2/token")
                    .setGrantType(GrantType.AUTHORIZATION_CODE)
                    .setClientId(CLIENT_ID)
                    .setClientSecret(CLIENT_SECRET)
                    .setRedirectURI(REDIRECT_URI)
                    .setCode(code)
                    .buildQueryMessage();


            OAuthClient client = new OAuthClient(new URLConnectionClient());

            OAuthJSONAccessTokenResponse oauthResponse = client.accessToken(oAuthRequest, OAuth.HttpMethod.POST);
        }

I've looked around but all the answers I've found didn't solve the problem.

Tried to use the other tokenresponse types.
Tried using .buildBodyMessage instead of .buildQueryMessage

I always get 1 of these ProblemExceptions:

Token request failed: unsupported_response_type, Invalid response! Response body is not application/json encoded

Token request failed: invalid_request, Missing parameters: access_token

I was hoping anyone has prior experience dealing with exact online, any help is appreciated.

Solution

Solution was to use an older version of the Oltu library. Using 0.31 works, but 1.0.1 does not. Strange behavior but maybe this will help someone in the future.